Implantable medical devices with increased immune tolerance, and methods for making and implanting

ABSTRACT

The present invention relates to the contacting of one or more surfaces of an implantable medical device with one or more diketopiperazines (DKPs).

CROSS REFERENCE TO RELATED APPLICATION

This application is a national stage application under 35 U.S.C. 371 and claims the benefit of PCT Application No. PCT/US2012/059483 having an international filing date of Oct. 10, 2012, which designated the United States, which PCT application claimed the benefit of priority under 35 U.S.C. § 119(e) to U.S. Provisional Patent Application No. 61/545,465, filed Oct. 10, 2011, the disclosures of which are incorporated herein by reference.

FIELD OF INVENTION

The present invention relates to the contacting one or more surfaces of an implantable medical device with one or more diketopiperazines (DKPs).

BACKGROUND OF THE INVENTION

Implantation of a medical device into a patient's body can trigger an abnormal immune response by the patient's body which is a threat to the acceptance of the implant and can result in device failure. For the patient, this can mean extended inflammation, higher risk of infection, and tissue build-up that may cause complications as well as discomfort. These effects slow patient recovery and often mean further medical intervention.

SUMMARY OF THE INVENTION

The present invention provides for a method to prepare an implantable medical device for implanation in a subject comprising contacting the device with a DKP.

The invention further provides for a method for implanting a medical device comprising implanting a medical device into a subject, wherein a surface of the device comprises a DKP.

In one aspect, the methods comprise a DKP comprising the following formula

wherein:

-   -   R¹ and R², which may be the same or different, each is:     -   (a) a side chain of an amino acid, wherein the amino acid is         glycine, alanine, valine, norvaline, α-aminoisobutyric acid,         2,4-diaminobutyric acid, 2,3-diaminobutyric acid, leucine,         isoleucine, norleucine, serine, homoserine, threonine, aspartic         acid, asparagine, glutamic acid, glutamine, lysine,         hydroxylysine, histidine, arginine, homoarginine, citrulline,         phenylalanine, p-aminophenylalanine, tyrosine, tryptophan,         thyroxine, cysteine, homocysteine, methionine, penicillamine or         ornithine; provided, however, that when R¹ is the side chain of         asparagine or glutamine, then R² cannot be the side chain of         lysine or ornithine, and when R¹ is the side chain of lysine or         ornithine, then R² cannot be the side chain of asparagine or         glutamine;     -   (b) R¹ is —CH₂—CH₂—CH₂— or —CH₂—CH(OH)—CH₂— and together with         the adjacent ring nitrogen forms proline or hydroxyproline, R²         is —CH₂—CH₂—CH₂— or —CH₂—CH(OH)—CH₂— and together with the         adjacent ring nitrogen forms proline or hydroxyproline, or both         R¹ and R² are each independently —CH₂—CH₂—CH₂— or         —CH₂—CH(OH)—CH₂— and together with the adjacent ring nitrogens         form proline or hydroxyproline; or     -   (c) a derivative of a side chain of an amino acid, wherein the         amino acid is one of those recited in (a), and the derivatized         side chain has:         -   (i) an —NH₂ group replaced by an —NHR³ or —N(R³)₂ group,             wherein each R³ may independently be a substituted or             unsubstituted alkyl, cycloalkyl, heterocycloalkyl, aryl,             alkylaryl, arylalkyl or heteroaryl;         -   (ii) an —OH group replaced by an —O—PO₃H₂ or —OR³ group,             wherein each R³ may independently be a substituted or             unsubstituted alkyl, cycloalkyl, heterocycloalkyl, aryl,             alkylaryl, arylalkyl or heteroaryl;         -   (iii) a —COOH group replaced by a —COOR³ group, wherein each             R³ may independently be a substituted or unsubstituted             alkyl, cycloalkyl, heterocycloalkyl, aryl, alkylaryl,             arylalkyl or heteroaryl;         -   (iv) a —COOH group replaced by a —CON(R⁴)₂ group, wherein             each R⁴ may independently be H or a substituted or             unsubstituted alkyl, cycloalkyl, heterocycloalkyl, aryl,             alkylaryl, arylalkyl or heteroaryl;         -   (v) an —SH group replaced by —S—S—CH₂—CH(NH₂)—COOH or             —S—S—CH₂—CH₂—CH(NH₂)—COOH;         -   (vi) a —CH₂— group replaced by a —CH(NH₂)— or a —CH(OH)—             group;         -   (vii) a —CH₃ group replaced by a —CH₂—NH₂ or a —CH₂—OH             group; and/or         -   (viii) an H which is attached to a carbon atom replaced by a             halogen; or             a physiologically-acceptable salt thereof.

The implantable medical device can be selected from a graft, catheter, stent, prosthetic, breast implant, pump, tube, pin, rod, screw, brace, plate and pace maker. In one aspect, the stent can be selected from a cardiac stent, an artery stent and a birth control stent. In another aspect, the prosthetic can be selected from an artificial hip, an artificial knee and an artificial ankle. In still another aspect, the pump can be an insulin pump. In yet another aspect, the implantable medical device is composed of material selected from metal, steal, titanium, glass, polymers, plastics and ceramics.

In one aspect, the DKP is adhered to the surface of the implantable medical device. In another aspect, the DKP is impregnated into the surface of the implantable medical device. In still another aspect, the DKP is coated onto the surface of the implantable medical device. In yet another aspect, the implantable medical device is contacted with a solution comprising a DKP, wherein the solution adheres to the device.

In some embodiments, the DKP that adheres to the surface of the implantable medical device, or is impregnated into the surface of the implantable medical device or coated onto the surface of the implantable medical device, can be in an amount of about 1 μM to about 500 μM. In still another aspect, the amount can be in an amount of about 50 μM to about 100 μM.

In some embodiments, the concentration of the DKP on a surface of the implantable medical device exposed to the body is about 1 ng/cm² to about 200 ng/cm². In another aspect, the concentration of the DKP on a surface of the implantable medical device exposed to the body is about 50 ng/cm².

The subject of the methods can be a mammal, including a human.

In some embodiments, the subject's immune tolerance to the device is increased by the presence of the DKP.

Another embodiment of the invention relates to an implantable medical device, wherein a surface of the device comprises a DKP. In one aspect, the device comprises a DKP comprising the following formula

wherein:

-   -   R¹ and R², which may be the same or different, each is:     -   (a) a side chain of an amino acid, wherein the amino acid is         glycine, alanine, valine, norvaline, α-aminoisobutyric acid,         2,4-diaminobutyric acid, 2,3-diaminobutyric acid, leucine,         isoleucine, norleucine, serine, homoserine, threonine, aspartic         acid, asparagine, glutamic acid, glutamine, lysine,         hydroxylysine, histidine, arginine, homoarginine, citrulline,         phenylalanine, p-aminophenylalanine, tyrosine, tryptophan,         thyroxine, cysteine, homocysteine, methionine, penicillamine or         ornithine; provided, however, that when R¹ is the side chain of         asparagine or glutamine, then R² cannot be the side chain of         lysine or ornithine, and when R¹ is the side chain of lysine or         ornithine, then R² cannot be the side chain of asparagine or         glutamine;     -   (b) R¹ is —CH₂—CH₂—CH₂— or —CH₂—CH(OH)—CH₂— and together with         the adjacent ring nitrogen forms proline or hydroxyproline, R²         is —CH₂—CH₂—CH₂— or —CH₂—CH(OH)—CH₂— and together with the         adjacent ring nitrogen forms proline or hydroxyproline, or both         R¹ and R² are each independently —CH₂—CH₂—CH₂— or         —CH₂—CH(OH)—CH₂— and together with the adjacent ring nitrogens         form proline or hydroxyproline; or     -   (c) a derivative of a side chain of an amino acid, wherein the         amino acid is one of those recited in (a), and the derivatized         side chain has:         -   (i) an —NH₂ group replaced by an —NHR³ or —N(R³)₂ group,             wherein each R³ may independently be a substituted or             unsubstituted alkyl, cycloalkyl, heterocycloalkyl, aryl,             alkylaryl, arylalkyl or heteroaryl;         -   (ii) an —OH group replaced by an —O—PO₃H₂ or —OR³ group,             wherein each R³ may independently be a substituted or             unsubstituted alkyl, cycloalkyl, heterocycloalkyl, aryl,             alkylaryl, arylalkyl or heteroaryl;         -   (iii) a —COOH group replaced by a —COOR³ group, wherein each             R³ may independently be a substituted or unsubstituted             alkyl, cycloalkyl, heterocycloalkyl, aryl, alkylaryl,             arylalkyl or heteroaryl;         -   (iv) a —COOH group replaced by a —CON(R⁴)₂ group, wherein             each R⁴ may independently be H or a substituted or             unsubstituted alkyl, cycloalkyl, heterocycloalkyl, aryl,             alkylaryl, arylalkyl or heteroaryl;         -   (v) an —SH group replaced by —S—S—CH₂—CH(NH₂)—COOH or             —S—S—CH₂—CH₂—CH(NH₂)—COOH;         -   (vi) a —CH₂— group replaced by a —CH(NH₂)— or a —CH(OH)—             group;         -   (vii) a —CH₃ group replaced by a —CH₂—NH₂ or a —CH₂—OH             group; and/or         -   (viii) an H which is attached to a carbon atom replaced by a             halogen; or             a physiologically-acceptable salt thereof.

The device can be selected from a graft, catheter, stent, prosthetic, breast implant, pump, tube, pin, rod, screw, brace, plate and pace maker. In yet another aspect, the device is composed of material selected from metal, steal, titanium, glass, polymers, plastics and ceramics.

In one aspect, the DKP is adhered to the surface of the device. In another aspect, the DKP is impregnated into the surface of the device. In still another aspect, the DKP is coated onto the surface of the device. In yet another aspect, the device is contacted with a solution comprising a DKP, wherein the solution adheres to the device.

In some embodiments, the DKP that adheres to the surface of the device, or is impregnated into the surface of the device or coated onto the surface of the device, can be in an amount of about 1 μM to about 500 μM. In still another aspect, the DKP amount can be in an amount of about 50 μM to about 100 μM.

In some embodiments, the concentration of the DKP on a surface of the device exposed to the body is about 1 ng/cm² to about 200 ng/cm². In another aspect, the concentration of the DKP on a surface of the device exposed to the body is about 50 ng/cm².

DESCRIPTION OF THE INVENTION

The present invention relates to the contacting (such as by coating, impregnating, etc.) of one or more surfaces of an implantable medical device with one or more diketopiperazines (DKPs). DKPs can suppress the immune response of a subject against the implanted medical device and can be referred to as immunomodulatory DKPs. By the introduction of DKPs to a surface of an implanted device, the problems associated with immune response against such devices (device failure and patient complications) can be reduced. Without being bound by theory, by coating or contacting an implantable medical device with a DKP, it is believed that the presence of the DKP increases the subject's immune tolerance to the device.

Various embodiments of the present invention include a method to prepare an implantable medical device in a subject by contacting the device with a DKP. Another embodiment is a method for implanting a medical device by implanting a medical device into a subject, wherein a surface of the device comprises a DKP. A further embodiment of the present invention is an implantable medical device, wherein a surface of the device comprises a DKP.

To increase immune tolerance of an implantable medical device and/or for implanting a medical device, the device and/or the surface of the device can be contacted by the diketopiperazine (DKP) of the present invention having the following formula:

wherein:

-   -   R¹ and R², which may be the same or different, each is:     -   (a) a side chain of an amino acid, wherein the amino acid is         glycine, alanine, valine, norvaline, α-aminoisobutyric acid,         2,4-diaminobutyric acid, 2,3-diaminobutyric acid, leucine,         isoleucine, norleucine, serine, homoserine, threonine, aspartic         acid, asparagine, glutamic acid, glutamine, lysine,         hydroxylysine, histidine, arginine, homoarginine, citrulline,         phenylalanine, p-aminophenylalanine, tyrosine, tryptophan,         thyroxine, cysteine, homocysteine, methionine, penicillamine or         ornithine; provided, however, that when R¹ is the side chain of         asparagine or glutamine, then R² cannot be the side chain of         lysine or ornithine, and when R¹ is the side chain of lysine or         ornithine, then R² cannot be the side chain of asparagine or         glutamine;     -   (b) R¹ is —CH₂—CH₂—CH₂— or —CH₂—CH(OH)—CH₂— and together with         the adjacent ring nitrogen forms proline or hydroxyproline         and/or R² is —CH₂—CH₂—CH₂— or —CH₂—CH(OH)—CH₂— and together with         the adjacent ring nitrogen forms proline or hydroxyproline; or     -   (c) a derivative of a side chain of an amino acid, wherein the         amino acid is one of those recited in (a), and the derivatized         side chain has:         -   (i) an —NH₂ group replaced by an —NHR³ or —N(R³)₂ group,             wherein each R³ may independently be a substituted or             unsubstituted alkyl, cycloalkyl, heterocycloalkyl, aryl,             alkylaryl, arylalkyl or heteroaryl;         -   (ii) an —OH group replaced by an —O—PO₃H₂ or —OR³ group,             wherein each R³ may independently be a substituted or             unsubstituted alkyl, cycloalkyl, heterocycloalkyl, aryl,             alkylaryl, arylalkyl or heteroaryl;         -   (iii) a —COOH group replaced by a —COOR³ group, wherein each             R³ may independently be a substituted or unsubstituted             alkyl, cycloalkyl, heterocycloalkyl, aryl, alkylaryl,             arylalkyl or heteroaryl;         -   (iv) a —COOH group replaced by a —CON(R⁴)₂ group, wherein             each R⁴ may independently be H or a substituted or             unsubstituted alkyl, cycloalkyl, heterocycloalkyl, aryl,             alkylaryl, arylalkyl or heteroaryl;         -   (v) an —SH group replaced by —S—S—CH₂—CH(NH₂)—COOH or             —S—S—CH₂—CH₂—CH(NH₂)—COOH;         -   (vi) a —CH₂— group replaced by a —CH(NH₂)— or a —CH(OH)—             group;         -   (vii) a —CH₃ group replaced by a —CH₂—NH₂ or a —CH₂—OH             group; and/or         -   (viii) an H which is attached to a carbon atom replaced by a             halogen; or             a physiologically-acceptable salt thereof.

By “replaced” is meant that, with reference to the formula of an amino acid side chain, the specified group is replaced by the other specified group. For instance, the formula of the isoleucine side chain is —CH(CH₃)—CH₂—CH₃. If the terminal —CH₃ group is replaced with a —CH₂—OH group, then the formula of the resulting derivatized isoleucine side chain would be —CH(CH₃)—CH₂—CH₂—OH. As another example, the formula of the alanine side chain is —CH₃. If one of the hydrogen atoms is replaced by a chlorine atom, then the resulting derivatized alanine side chain would be —CH₂—Cl. Note that the side chain of glycine is —H and, if this H is replaced by a chlorine (or other halogen) atom, the resulting side chain will —Cl, with the chlorine atom attached to the ring carbon (e.g., R¹═—Cl)

Preferred are diketopiperazines wherein R¹, R² or both is the side chain of aspartic acid or glutamic acid or a derivative of such a side chain wherein the —COOH group is replaced by a —COOR³ group or a —CON(R⁴)₂ group, wherein R³ and R⁴ are defined above. Of this group of compounds, most preferred are diketopiperazines comprising the side chains of aspartic acid and alanine (Asp-Ala DKP or DA-DKP), the side chains of glutamic acid and alanine (Glu-Ala DKP or EA-DKP), the side chains of tyrosine and aspartic acid (Tyr-Asp DKP or YD-DKP), the side chains of tyrosine and glutamic acid (Tyr-Glu DKP or YE-DKP) and derivatives of the aspartic acid or glutamic acid side chains of these four diketopiperazines wherein the —COOH group is replaced by a —COOR³ group or a —CON(R⁴)₂ group, wherein R³ and R⁴ are defined above.

Also, preferred are diketopiperazines wherein R¹ and R² are both hydrophobic side chains (e.g., the side chain of phenylalanine) or hydrophobic side chain derivatives. By “hydrophobic side chain derivative” is meant that the derivatized side chain which is hydrophobic. In particular, preferred are diketopiperzines wherein R¹ and/or R², which may be the same or different, each is the side chain of glycine, alanine, valine, norvaline, α-aminobutyric acid, leucine, isoleucine, norleucine or phenylalanine, and/or R¹ and/or R² is —CH₂—CH₂—CH₂— and together with the adjacent nitrogen atom(s) form proline. Of this group of compounds, most preferred are the diketopiperazines comprising the side chains of glycine and leucine (Gly-Leu DKP or GL-DKP), proline and phenylalanine (Pro-Phe DKP or PF-DKP), and alanine and proline (Ala-Pro DKP or AP-DKP).

Additional preferred diketopiperazines are those wherein R¹, R² or both is the side chain of methionine, the side chain of arginine or a derivative of these side chains. Most preferred of this group is a diketopiperazine wherein R¹ is the side chain of methionine and R² is the side chain of arginine (Met-Arg DKP or MR-DKP).

By “side chain” of an amino acid is meant that portion of the amino acid attached to the common NH₂—CH—COOH backbone of all of the amino acids listed above. For instance, the side chain of glycine is —H, the side chain of alanine is —CH₃, and the side chain of serine is —CH₂OH.

By “hydrophobic” is meant a side chain or side chain derivative that is uncharged at physiological pH and is repelled by an aqueous solution.

By “alkyl” is meant a saturated straight-chain or branched hydrocarbon containing 1-10 carbon atoms, preferably 1-6, carbon atoms. “Lower alkyl” means a saturated straight-chain or branched hydrocarbon containing 1-6 carbon atoms.

By “cycloalkyl” is meant a saturated cyclic hydrocarbon containing at least one ring, each ring containing at least three carbon atoms. Preferably, the cycloalkyl contains one ring of 4-8 carbon atoms.

By “heterocycloalkyl” is meant a cycloalkyl having one or more of the ring carbon atoms of at least one of the rings replaced by an O, S or N.

By “aryl” is meant an aromatic group having at least one aromatic ring (e.g., phenyl).

By “alkylaryl” is meant a lower alkyl having an H replaced by an aryl (e.g., —CH₂—C₆H₅ or —CH₃CH(C₆H₅)CH₃).

By “arylalkyl” is meant an aryl having an H replaced by a lower alkyl (e.g., —C₆H₄—CH₃).

By “heteroaryl” is meant an aryl having one or more of the ring carbon atoms of at least one of the rings replaced by an O, S or N.

By “substituted” is meant that the moiety is substituted with one or more substituents selected from the following group: —OH, NH₂, —SH, —COOH and/or a halogen atom.

By “halogen” is meant chlorine, fluorine, bromine or iodine. Preferred is chlorine or bromine.

Methods of making diketopiperazines are well known in the art, and these methods may be employed to synthesize the diketopiperazines of the invention. See, e.g., U.S. Pat. Nos. 4,694,081, 5,817,751, 5,990,112, 5,932,579 and 6,555,543, US Patent Application Publication Number 2004/0024180, PCT applications WO 96/00391 and WO 97/48685, and Smith et al., Bioorg. Med. Chem. Letters, 8, 2369-2374 (1998), the complete disclosures of which are incorporated herein by reference.

For instance, diketopiperazines can be prepared by first synthesizing dipeptides. The dipeptides can be synthesized by methods well known in the art using L-amino acids, D-amino acids or a combination of D- and L-amino acids. Preferred are solid-phase peptide synthetic methods. Of course, dipeptides are also available commercially from numerous sources, including DMI Synthesis Ltd., Cardiff, UK (custom synthesis), Sigma-Aldrich, St. Louis, Mo. (primarily custom synthesis), Phoenix Pharmaceuticals, Inc., Belmont, Calif. (custom synthesis), Fisher Scientific (custom synthesis) and Advanced ChemTech, Louisville, Ky.

Once the dipeptide is synthesized or purchased, it is cyclized to form a diketopiperazine. This can be accomplished by a variety of techniques. For example, U.S. Patent Application Publication Number 2004/0024180 describes a method of cyclizing dipeptides. Briefly, the dipeptide is heated in an organic solvent while removing water by distillation. Preferably, the organic solvent is a low-boiling azeotrope with water, such as acetonitrile, allyl alcohol, benzene, benzyl alcohol, n-butanol, 2-butanol, t-butanol, acetic acid butylester, carbon tetrachloride, chlorobenzene chloroform, cyclohexane, 1,2-dichlorethane, diethylacetal, dimethylacetal, acetic acid ethylester, heptane, methylisobutylketone, 3-pentanol, toluene and xylene. The temperature depends on the reaction speed at which the cyclization takes place and on the type of azeotroping agent used. The reaction is preferably carried out at 50-200° C., more preferably 80-150° C. The pH range in which cyclization takes place can be easily determined by the person skilled in the art. It will advantageously be 2-9, preferably 3-7. When one or both of the amino acids of the dipeptide has, or is derivatized to have, a carboxyl group on its side chain (e.g., aspartic acid or glutamic acid), the dipeptide is preferably cyclized as described in U.S. Pat. No. 6,555,543. Briefly, the dipeptide, with the side-chain carboxyl still protected, is heated under neutral conditions. Typically, the dipeptide will be heated at from about 80° C. to about 180° C., preferably at about 120° C. The solvent will be a neutral solvent. For instance, the solvent may comprise an alcohol (such as butanol, methanol, ethanol, and higher alcohols, but not phenol) and an azeotropic co-solvent (such as toluene, benzene, or xylene). Preferably, the alcohol is butan-2-ol, and the azeotropic co-solvent is toluene. The heating is continued until the reaction is complete, and such times can be determined empirically. Typically, the dipeptide will be cyclized by refluxing it for about 8-24 hours, preferably about 18 hours. Finally, the protecting group is removed from the diketopiperazine. In doing so, the use of strong acids (mineral acids, such as sulfuric or hydrochloric acids), strong bases (alkaline bases, such as potassium hydroxide or sodium hydroxide), and strong reducing agents (e.g., lithium aluminum hydride) should be avoided, in order to maintain the chirality of the final compound.

Dipeptides made on solid phase resins can be cyclized and released from the resin in one step. See, e.g., U.S. Pat. No. 5,817,751. For instance, the resin having an N-alkylated dipeptide attached is suspended in toluene or toluene/ethanol in the presence of acetic acid (e.g., 1%) or triethylamine (e.g., 4%). Typically, basic cyclization conditions are preferred for their faster cyclization times.

To prepare the diketopiperazine of formula I wherein the amino acid side chains are derivatized, amino acid derivatives can be used in the synthesis of the dipeptides, the dipeptides can be derivatized and/or the diketopiperazines can be derivatized, as is known in the art. See, e.g., those references cited above.

Other methods of cyclizing dipeptides and of making diketopiperazines are known in the art and can be used in the preparation of diketopiperazines useful in the practice of the invention. See, e.g., those references listed above. In addition, many diketopiperazines suitable for use in the present invention can be made as described below from proteins and peptides. Further, diketopiperazines for use in the practice of the invention can be obtained commercially from, e.g., DMI Synthesis Ltd., Cardiff, UK (custom synthesis).

The diketopiperazines of formula I include all possible stereoisomers than can be obtained by varying the configuration of the individual chiral centers, axes or surfaces. In other words, the diketopierazines of formulas I and II include all possible diastereomers, as well as all optical isomers (enantiomers).

The physiologically-acceptable salts of the diketopiperazines of the invention may also be used in the practice of the invention. Physiologically-acceptable salts include conventional non-toxic salts, such as salts derived from inorganic acids (such as hydrochloric, hydrobromic, sulfuric, phosphoric, nitric, and the like), organic acids (such as acetic, propionic, succinic, glycolic, stearic, lactic, malic, tartaric, citric, glutamic, aspartic, benzoic, salicylic, oxalic, ascorbic acid, and the like) or bases (such as the hydroxide, carbonate or bicarbonate of a pharmaceutically-acceptable metal cation or organic cations derived from N,N-dibenzylethylenediamine, D-glucosamine, or ethylenediamine). The salts are prepared in a conventional manner, e.g., by neutralizing the free base form of the compound with an acid.

It has been found that diketopiperazines suitable for use in the present invention are present in some commercially-available intravenous pharmaceutical compositions containing albumin, immunoglobulin and erythropoietin. The diketopiperazines present in these pharmaceutical preparations are formed by the heating steps often used in the manufacture of these pharmaceutical compositions. The heating results in cleavage and cyclization of the two N-terminal and/or two C-terminal amino acids of the proteins to form diketopiperazines.

Accordingly, diketopiperazines for use in the present invention can be prepared by heating solutions of albumin, immunoglobulin, erythropoietin and other proteins and peptides. For example, a solution of albumin, immunoglobulin, erythropoietin or another protein or peptide in phosphate buffer at neutral pH is prepared. Preferably, the solution is a concentrated solution (e.g., about 100-500 mM) to achieve protonation of the N-terminal and/or C-terminal amino acid. The solution is heated at 60° C. for from about 2 hours to several days, preferably about 4 days, to cause formation of the diketopiperazines. Denaturation of the protein should, preferably, be avoided. This can be accomplished by using shorter times and/or by adding caprylic acid or N-acetyl tryptophan at about 0.02 M for each.

Diketopiperazines for use in the present invention can also be prepared by contacting a solution of albumin, immunoglobulin, erythropoietin or another protein or peptide with an enzyme that can cleave the two N-terminal amino acids from the protein or peptide (e.g., dipeptidyl peptidases) or an enzyme that can cleave the two C-terminal amino acids from the protein or peptide (e.g., carboxypeptidases). Suitable dipeptidyl peptidases and carboxypeptidases are available commercially from, e.g., Sigma. The reaction should be conducted at pH 6-8, preferably in a buffer, such as phosphate buffer, at a temperature high enough to speed the reaction but not so high that the protein is denatured (e.g., 37° C.).

The amino acid sequences of numerous proteins and peptides are known, and a protein or peptide with the desired N-terminal and/or C-terminal sequence can be chosen to give the desired diketopiperazine(s) using either method. Also, peptides with a desired sequence can be synthesized by well known methods and used.

The diketopiperazines can be purified from solutions containing them, including from the commercially-available pharmaceutical compositions comprising albumin, immunoglobulin and erythropoietin, by well known methods, such as size-exclusion chromatography (e.g., Centricon filtration), affinity chromatography (e.g., using a column of beads having attached thereto an antibody or antibodies directed to the desired diketopiperazine(s) or an antibody or antibodies directed to the truncated protein or peptide), anion exchange or cation exchange. The purified diketopiperazines can be used and incorporated into pharmaceutical compositions as described above.

A DA-DKP composition of the present invention can be prepared from solutions containing DA-DKP, including from the commercially-available pharmaceutical compositions comprising albumin, such as human serum albumin, by well known methods, such as ultrafiltration, chromatography (size-exclusion chromatography (e.g., Centricon filtration), affinity chromatography (e.g., using a column of beads having attached thereto an antibody or antibodies directed to the desired diketopiperazine(s) or an antibody or antibodies directed to the truncated protein or peptide), anion exchange or cation exchange), sucrose gradient centrifugation, chromatography, salt precipitation, or sonication, that will remove some or all of the albumin in the solution. The resultant DA-DKP-containing composition can be used and incorporated into compositions used to coat, impregnate or cover the implantable medical devices of the present invention.

Using ultrafilration as a separation method, a human serum albumin composition can be passed over an ultrafiltration membrane having a molecular weight cut-off that retains the albumin while the DA-DKP passes into the resulting filtrate or fraction. This filtrate may comprise components having molecular weights less than about 50 kDA, less than about 40 kDa, less than 30 kDa, less than about 20 kDa, less than about 10 kDa, less than about 5 kDa, less than about 3 kDa. Preferably, the filtrate comprises components having molecular weights less than about 5 Da (also referred to as “<5000 MW”). This <5000 MW fraction or filtrate contains DA-DKP which is formed after the dipeptide aspartate-alanine is cleaved from albumin and subsequently cyclized into the diketopiperazine.

Implantable medical devices of the present invention are devices which can be implanted into a subject. For example, such devices can be a graft, a catheter, stent, prosthetic, implant (such as a breast implant), pump, tubes, pins, rods, screws, brace, plates or pace maker. Stents can include but are not limited cardiac stents and artery stents (for example for use in widening arteries and to improve blood flow), and birth control stents (such as Essure®). Prosthetics can include but are not limited to artificial hip(s), artificial knee(s) or artificial ankle(s). Pumps can include but are not limited to insulin pumps.

The implantable medical devices of the present invention can be composed of one or more various materials. For example, the material can be metal, steel, titanium, glass, polymers, plastics or ceramics.

The diketopiperazines of the invention can be adhered to, impregnated into or coated onto the surface of the implantable medical devices. For example, an implanted medical device can be contacted with a DKP containing solution, wherein the solution adheres to or impregnates into or coats the implantable medical device. The concentration of the DKP that adheres to or is coated onto the surface of the implanted medical device can be in a range with a lower endpoint of about 1 μM, about 5 μM, about 10 μM, about 20 μM, about 30 μM, about 40 μM, about 50 μM, about 60 μM, about 70 μM, about 80 μM, about 90 μM, about 100 μM, about 110 μM, about 120 μM, about 130 μM, about 140 μM, about 150 μM, about 160 μM, about 170 μM, about 180 μM, about 190 μM, or about 200 μM. In addition, the concentration of the DKP that adheres to or is coated onto the surface of the implanted medical device can be in a range with an upper endpoint of about 500 μM, about 475 μM, about 450 μM, about 425 μM, about 400 μM, about 375 μM, about 350 μM, about 325 μM, about 320 μM, about 310 μM, about 300 μM, about 290 μM, about 280 μM, about 270 μM, about 260 μM, about 250 μM, about 240 μM, about 230 μM, about 220 μM, or about 210 μM.

In a further embodiment of the present invention, the concentration of the DKP on a surface of a medical device that is exposed to the body when implanted can be in a range with a lower endpoint of about 1 ng/cm², about 5 ng/cm², about 10 ng/cm², about 15 ng/cm², about 20 ng/cm², about 25 ng/cm², about 30 ng/cm², about 35 ng/cm², about 40 ng/cm², about 45 ng/cm², about 50 ng/cm², about 55 ng/cm², about 60 ng/cm², about 65 ng/cm², about 70 ng/cm², about 75 ng/cm², about 80 ng/cm², about 85 ng/cm², about 90 ng/cm², about 95 ng/cm², or about 100 ng/cm². Preferably, the concentration of the DKP on a surface of a medical device that is exposed to the body when implanted is about 50 ng/cm². In addition, the concentration of the DKP on a surface of a medical device that is exposed to the body when implanted can be in a range with an upper endpoint of about 200 ng/cm², about 195 ng/cm², about 190 ng/cm², about 185 ng/cm², about 180 ng/cm², about 175 ng/cm², about 170 ng/cm², about 165 ng/cm², about 160 ng/cm², about 155 ng/cm², about 150 ng/cm², about 145 ng/cm², about 140 ng/cm², about 135 ng/cm², about 130 ng/cm², or about 125 ng/cm².

Subjects of the present invention can be a mammal, such as a rabbit, goat, dog, cat, horse or human. Preferably, the subject is a human.

As used herein, “a” or “an” means one or more.

As used herein, “comprises” and “comprising” include within their scope all narrower terms, such as “consisting essentially of” and “consisting of” as alternative embodiments of the present invention characterized herein by “comprises” or “comprising”. In regard to use of “consisting essentially of”, this phrase limits the scope of a claim to the specified steps and materials and those that do not materially affect the basic and novel characteristics of the invention disclosed herein.

Additional objects, advantages and novel features of the present invention will become apparent to those skilled in the art by consideration of the following non-limiting examples. The following experimental results are provided for purposes of illustration and are not intended to limit the scope of the invention.

EXAMPLES Example 1

This example shows the results of an analysis of biofilms on extracted orthopedic devices to determine if the presence of a diketopiperazine is correlated with bacterial colonization. Bacteria use small molecular weight N-acylhomoserine lactones and diketopiperazines to initiate biofilm formation and regulate colony growth. An Aspartate, Alanine-Diketopiperazine (DA-DKP) formed by the cleavage and cyclization of the N-terminal amino acids of human serum albumin has previously been demonstrated to be immunomodulatory for memory but not naive human T lymphocytes.

Methods:

This study was an institutional review board (IRB) approved study. Twenty two patients undergoing hardware removal were enrolled. The removed orthopedic devices were stripped of surface biofilm using methanol/ammonium formate. The ≤3 kD MW material was collected and diketopiperazine levels analyzed using anion exchange high pressure liquid chromatography coupled to negative electrospray ionization mass spectrometry.

Results:

The thirty-three patients ranged in age from 6 to 91 years, with a mean of 54. There were fifteen males and eighteen females. Ten devices were reported by the clinical laboratory to be culture positive. In five cases the main organism was Staphylococcus. In one of the three cases Bacteroides and Streptococcus species were also isolated. In all thirty-three cases detectable amounts of DA-DKP were identified with a mean level of 120 ng/ml. Higher amounts of DA-DKP (9.75-235 ng/ml) were detected in the culture positive devices versus the culture negative (1.78-34.7 ng/ml). In addition, one device removed from a case with osteomyelitis had a DA-DKP content of 3,063 ng/ml. (see Table 1).

Conclusion:

DA-DKP is an important immune modulator in biofilm formation on orthopedic implants. Its presence in biofilms found on extracted orthopedic devices suggests innate physiologic mechanisms conferring tolerance to the implanted device possibly correlated to the presence of inflammation/rejection reactions.

TABLE 1 Study Group DA-DKP amounts Age Sex of Concentraton of subject of sub- F = female DA-DKP ject M = male Device Removed Culture Results ng/ml 73 F Pin (hip) None 4.63 66 F Rod + Screws Negative 19.7 (hip) 89 F Rod + Screws Staph (positive) 87.0 (hip) 74 M Staple (knee) None 3.03 67 F Septic hip prosth. Staph aureus 84.8 44 M Plate (clavicle) None 2.40 45 F Rod + Screws Negative 30.9 (spine) 87 F Screws None 19.9 (hip arthritis) 33 M Rod + Screws None 6.03 (knee) 45 M Rod + Screws None 9.05 (ulna) 31 F Rod + Screws Bacteroides + 53.7 (ankle) Strep 52 F Brace + Screws None 9.02 (tibia) 58 F Screws (femur) Staph (positive) 28.4 74 M Brace (clavicle) Negative 7.02 6 M Plate + Screws None 22.4 60 F Rod Negative 3,063 (osteomyelitis tibia) 58 F Hip Prosth. Negative 23.0 66 F Rod (femoral) Staph + Strep 235 45 M Rod + Screws Gram+ 12.9 (tibia) 55 M Nails (femoral) Gram+ 70.4 54 F Ankle Prosth. Negative 34.7 24 M Screws (tibia) Gram+ 9.75 91 F Screws (hip) None 3.91 44 M Plate + Screws None 14.2 (ankle) 46 F Screws (ankle) None 9.32 24 M Screws (femur) Staph aureus 53.1 68 F Knee Prosth. Negative 1.78 56 F Screws (knee) None 3.41 41 F Brace + Screws Yeast 20.4 (ankle) 61 M Screws (femur) Negative 4.21 34 M Plate + Screws Negative 9.78 (radius) 77 M Plate + Rod (hip) None 2.13 28 M Plates + Screw None 12.7 (ankle)

Example 2

Isolation and characterization of peptides and proteins from endotracheal tubes. The results of this example further demonstrate that DKPs form on implantable medical devices such as endotracheal tubes, when they are implanted within a subject. The presence of the DKPs on these tubes helps the subject to confer tolerance to the tubes. This again demonstrates the unique finding of coating implantable medical devices, such as entracheal tubes, with DPKs prior to implantation so as to increase the subject's immune tolerance and/or to decrease a subject's inflammatory response to the tube.

Endotracheal tubes discarded from mechanically ventilated trauma patients are collected into sterile biohazard pouches and transported immediately to the Trauma Research Lab. As controls for the absence of biofilms, discarded endotracheal tubes form surgical patients that were only used for a few hours during surgery were used.

Method

Biofilm and/or mucus is stripped from the proximal ends of endotracheal tubes by placing in a sterile centrifuge tube containing 1-2 ml of chromatography each analysis buffer consisting of methanol 60% plus 50 mM ammonium formate 40% with extensive washing using a pipette and agitation on a vortexer. After the biofilm is stripped from the endotracheal tube, the sediment is pelleted by centrifugation and frozen for later analysis of bacterial content. The biofilm supernatant is collected for analysis of protein and large molecular width peptides. An aliquot of the biofilm supernatant is placed in an ultrafiltration spin column (Vivaspin 500, 3,000 MWCO, Sartorius, Hannover, Germany) for centrifugation at 15,000×g. The filtrate is collected for analysis of <3 kD molecular weight peptides.

Supernatants containing higher molecular weight material are analyzed by high performance liquid chromatography (HPLC, Waters, Milford, Mass., USA) coupled to positive electrospray ionization time of flight mass spectrometry (+ESI-TOF MS, Micromass, UK). Each supernatant is diluted 1:10 with dH₂O. 10 μL of each sample is injected onto a YMC-Pack Protein-PR, 150 mm×4.6 mm, 5 u, HPLC column heated at 50° C. (Waters, Milford, Mass., USA) using a 20 minute linear gradient method used water/0.1% trifluoroacetic acid (A) and acetonitrile/0.1% TFE (B). The output of the HPLC is split 1:20 (v:v) and injected into the mass spectrometer with a scan range of 500 to 3500 m.z, cone voltage of 30 eV, source temperature of 100° C., and gas temperature of 250° C. Albumin (a molecular standard) elutes at 8.15 minutes and is visualized as a charge envelope from 1100 to 2500 m/z representing +44 to +26 charges. The spectrum is the deconvolved to the uncharged parent mass using MaxEnt 1 (Micromass, UK). The parent mass spectrum is then integrated and relative proportions of each species were calculated.

50 μl of each of the <3000-Da filtrate fractions of bioflim supernatant is injected into high performance liquid chromatography (HPLC, 2795 system, Waters, Mass.) coupled to a mass spectrometer (LCT-TOF, Micromass, UK), and quantified using a storage anion exchange column (Supelcosil, SAX1 250 mm×4.6 mm, Supelco) and a 70:30 v/v methanol/water with 25 mM ammonium acetate (Sigma Aldrich, St. Lois, Mo.) as the mobile phase in an isocratic mode at 1 ml/min. The output of the HPLC is split 1:20 (v/v) and injected into the mass spectrometer using negative electrospray ionization (−ESI MS) with a scan ranges of 80-1000 m/z, cone voltage of 30 eV, source temperature of 100° C. and a gas temperature of 250° C. DA-DKP, as a molecular standard, is measure by monitoring the mass 185 in time which corresponds to DA-DKP minus a single proton (—H+). DA-DKP elutes at 5.8 mins and is quantified by integrating the area under the curve. The area was compared with a standard curve derived from synthetic DA-DKP standard (DMI Synthesis, Newport, Wales) of known concentrations (5000 ng/ml, 1000 ng/ml, 200 ng/ml, 40 ng/ml, 8 ng/ml). The calibration curve was found to be very linear in this range within R2 of 0.99998.

The concentration of DKP on over 100 endothracheal tubes as detected by the method described above is presented in Table 2. The DKP concentration ([DKP]) provided on Table 2 has already been adjusted per volume added to dissolve biofilm. The following are indicated on Table 2:

ID#: Subject identification number

Sex: Subject's sex either male (M) or female (F)

Age: Age in years of the subject

[DKP] ng/ml: The DKP concentration in ng/ml already adjusted per volume added to dissolve biofilm

Bacteria identified: Type of bacteria detected on endotracheal tube

Vent Days: The number of days the endotracheal tube was implanted with the subject

Protein identified: The proteins that were determined on the endotracheal tube

AIS: Abbreviated injury score/scale, with a score of 1 being a minor injury, 2=moderate, 3=serious, 4=severe, 5=critical, 6=maximum, 9=not further specified.

ISS: Injury severity score, assesses trauma severity and correlates with mortality, morbidity and hospitalization time after trauma.

GCS: Glascow coma score/scale-neurological scale to help assess the status of the central nervous system and used acutely to grade the severity of a subject's trauma and mental function.

GOS: Glascow outcome score/scale (R=rehabilitation; L=long term acute care; 1=dead; 5=good recovery)—a 5 point score given to victims of traumatic brain injury at some point in their recovery.

TABLE 2 DKP Concentration on Endotracheal Tubes [DKP] Vent Proteins ID # Sex Age ng/ml Bacteria Days ID AIS ISS GCS GOS  18 M 25 150.06 8 PRP1, 2 38 15 5 HIG2, AT5G1  24 M 47 607.73 S. pneumon 11 Defensin 3 20 15 R MRSA 1, 2, 3 LL-37, Lysozyme C  25 M 90 <20 3 Defensin 3 14 6 1 1, 2, 3 LL-37  28 F 22 <20 1 Defensin 3 21 7 R 1, 2, 3 LL-37  30 F 55 1,071.55 Enterob. 4 2 17 3 R Sakazakii  30-2 F 55 <20 Enterob. 4 2 17 3 R Sakazakii  31 M 60 1,402.85 9 S10A8 3 10 15 5  34 M 20 <20 H. influenza 30 5 45 3 R  35 F 71 116.29 7 4 30 6 L  36 M 46 1,580.08 Pneumothorax 11 3 34 9 R  36-2 M 46 <20 Pneumothorax 11 3 34 9 R  39 M 58 <20 5 4 29 15 L  41 M 35 72.53 K. oxytoca 20 3 43 3 L S. aureus  44 M 35 <20 8 4 25 4 5  45 M 17 34.09 S. marcesens 3 1 21 3 5  50 M 76 362.29 1 3 22  52 M 34 159.56 <1 2 17 12 R  53 M 21 156.85 <1 3 14 6 1  58 M 25 <20 36 5 29 15 L  60 M 15 124.82 1 1 41 5  70 M 28 104.63 4 3 26 3 R  79 M 73 33.48 K. oxytoca 8 4 L  87 M 49 79.92  90 F 56 103.79  96 F 49 637.7  97 M 30 1,752.89  98 F 24 952.71 102 M 32 1,311.48 106 F 80 1,083.15 108 F 59 2,648.23 109 M 20 629.67 114 M 76 379.51 121 F 84 2,325.85 123 M 15 8,009.14 129 M 27 500.95 131 F 65 16,194.74 132 M 32 282.84 133 F 48 480.59 138 M 49 137.37 140 F 81 567.2 143 M 28 426.93 145 M 68 1,655.73 149 M 21 58.68 149-2 M 21 749.03 150 M 31 111.68 151 M 50 389.23 152 M 25 134.8 153 F 51 272.45 156 M 29 25.45 157 F 18 634.13 158 M 51 2,183.93 161 M 77 386.28 161-2 M 77 691.98 162 M 18 364.63 163 M 63 107.4 164 F 15 69.15 166 F 18 856.74 169 F 30 <20 170 M 73 368.9 178 M 53 48.55 179 M 25 <20 182 M 67 1059.7 182-2 M 67 255.73 183 M 36 279.76 184 M 37 <20 190 M 34 624.44 191 M 29 2,207.58 191-2 M 29 798.37 192 M 66 <20 195 M 28 2,608.52 196 F 23 <20 198 M 35 404.87 200 M 33 816.38 202 M 67 <20 203 M 50 112.64 204 1,290.96 205 2,108.70 206 656.8 208 <20 209 276.96 210 76.19 211 76.98 212 <20 212-2 505.63 213 218.41 215 503.16 215-2 322.54 216 163.25 219 12,019.74 221 177.19 222 155.14 225 247.88 228 190.86 229 92.4 231 243.68 233 72.03 234 22.96 235 356.11 235-2 68.11 237 509.7 239 1,620.48 Surg 2,648.55 <1 001 Surg 500.22 <1 002 Surg 56.74 <1 003 Surg 505.67 <1 004 Surg <20 <1 005 Surg F 83 89.23 92 Surg F 83 67.87 92-2 R 2235.63 111 R 1216.05 113

While various embodiments of the present invention have been described in detail, it is apparent that modifications and adaptations of those embodiments will occur to those skilled in the art. It is to be expressly understood, however, that such modifications and adaptations are within the scope of the present invention, as set forth in the following exemplary claims. 

What is claimed:
 1. An implantable medical device, wherein a surface of the device comprises DA-DKP.
 2. The device of claim 1, wherein the implantable medical device is selected from the group consisting of a graft, catheter, stent, prosthetic, breast implant, pump, tube, pin, rod, screw, brace, plate and pace maker.
 3. The device of claim 1, wherein the implantable medical device is composed of a material selected from the group consisting of metal, steel, titanium, glass, polymers, plastics, and ceramics.
 4. The device of claim 1, wherein the DA-DKP is adhered to the surface of the device.
 5. The device of claim 1, wherein the DA-DKP is impregnated into the surface of the device.
 6. The device of claim 1, wherein the DA-DKP is coated onto the surface of the device.
 7. The device of claim 1, produced by contacting the device with a solution comprising DA-DKP, wherein the solution adheres to the device.
 8. The device of claim 7, wherein the DA-DKP is present in the solution in an amount of about 1 μM to about 500 μM.
 9. The device of claim 7, wherein the DA-DKP is present in the solution in an amount of about 50 μM to about 100 μM.
 10. The device of claim 1, wherein the concentration of the DA-DKP on a surface of the implantable medical device exposed to the body is about 1 ng/cm² to about 200 ng/cm².
 11. The device of claim 1, wherein the concentration of the DA-DKP on a surface of the implantable medical device exposed to the body is about 50 ng/cm².
 12. The device of claim 1, wherein the implantable medical device is selected from the group consisting of a prosthetic, breast implant, pump, tube, pin, rod, screw, brace, plate and pace maker.
 13. A method to prepare the implantable medical device of claim 1 for implantation in a subject, comprising contacting the device with a diketopiperazine (DKP), wherein the DKP is DA-DKP.
 14. A method for implanting a medical device comprising implanting the medical device of claim 1 into a subject, wherein a surface of the device comprises DA-DKP. 